When harvesting windrowed crops with a pick-up attachment mounted on the header of a combine harvester or when cutting the crops close to the ground surface with a direct-cut attachment, stones and other hard foreign objects inadvertently may be picked up and fed to the threshing mechanism, which thereby is exposed to severe damage. To prevent these foreign objects from entering the threshing mechanism, combine harvesters commonly are equipped with a trough-shaped stone trap disposed between the threshing mechanism and the normal crop elevator which conveys crop material from the crop gathering attachment to this threshing mechanism. Foreign objects which are fed towards the threshing mechanism are hit by threshing bars thereof and, as a result, are projected into the stone trap.
The crop elevator commonly is in the form of a feeder housing enclosing a chain-and-slat apron conveyor which entrains crop material and feeds the same rearwardly through a discharge opening of the feeder housing proximate to the threshing mechanism. The stone trap thus is positioned with its inlet opening generally at the transition between said discharge opening and the threshing mechanism with the stone trap itself being positioned below the plane of that transition. In other words, as seen from the front of the combine, the stone trap is positioned below the rearward end of the feeder housing.
Details of a combine harvester equipped with a conventional stone trap can be taken from EP-A-0.096.923, the content of which is included herein by reference.
As can be seen from the aforementioned prior art document, the stone trap obstructs access from underneath the crop elevator to the grain pan; said grain pan being disposed beneath the threshing mechanism and extending rearwardly into the machine from the vicinity of the rear wall of the stone trap for conveying threshed crop material, received from the threshing mechanism, to the cleaning mechanism for further processing. During operation in wet crop conditions, dirt may accumulate on the surface of the grain pan and, when this occurs, cleaning of the grain pan becomes necessary. Access to the grain pan for removing accumulated dirt normally is possible only from the rear of the machine by reaching over the cleaning apparatus. This is a difficult task and, as a consequence, there is substantial operator reluctance to carry out this grain pan cleaning as frequently as is required.
Access to the grain pan from the forward end of the machine at a location beneath the discharge end of the crop elevator is possible in the arrangements according to CA-A-991.937, DE-A-2.013.289 and DE-A-2.523.715 by providing means which permit the grain pan or parts thereof to swing downwardly for servicing. However, this is a complicated and hence also an expensive solution.